US patent application 2009/0209303 A1 discloses a wireless headset with a thermoelectric device, a regulator and an energy storage element, e.g. a rechargeable battery. One side of the thermoelectric device is thermally connected through thermally conductive material, e.g. a high density conductive polymer, to the user's body and is thus subjected to a temperature close to the temperature of the user's skin, whereas the other side is thermally connected through thermally conductive material to solar cells subjected to ambient temperature. The thermoelectric device converts a temperature difference between the user's skin and the solar cells into an electric current, which is supplied to the energy storage element through the regulator in order to provide power for operation of the wireless headset.
The thermally conductive material occupies a relatively large portion of the outside surface of the wireless headset.
German patent application DE 10 232 376 A discloses a thermoelectric element and the use of it for powering a hearing aid. The thermoelectric element comprises a stack of electrically conductive and electrically insulating layers, and the electrically conductive layers may comprise an electrically conductive polymer.
European patent application EP 2 200 347 A2 discloses a hearing aid having electrodes for measuring an electroencephalogram (EEG). The electrodes may be manufactured in the surface of a hearing aid shell. The hearing aid may further have a thermo element for measuring the body temperature of the hearing-aid user and being located where the hearing aid meets the skin surface.
European patent application EP 2 299 731 A1 discloses a listening device wherein charging pads for charging a rechargeable battery are arranged on a housing portion intended for placement in the ear canal during use of the listening device.
The electrodes and charging pads disclosed in the above mentioned prior art also occupy significant portions of the outside surfaces of the respective device housings.